Biochemical indicators of cardiac and renal function in a healthy elderly population

Meteorin-like protein is associated with a higher risk profile and predicts a worse outcome in patients with STEMI

INTRODUCTION AND OBJECTIVES

Meteorin-like protein (Metrnl) is a cytokine involved in the attenuation of inflammation. In patients with heart failure, high levels of this biomarker are associated with a worse outcome. In this study, we evaluated the circulating levels and prognostic value of Metrnl in patients with ST-segment elevation myocardial infarction (STEMI).

METHODS

We enrolled STEMI patients undergoing primary percutaneous coronary intervention. Circulating Metrnl levels were measured in peripheral blood 12hours after symptom onset. The primary endpoint was a composite of all-cause mortality or nonfatal myocardial infarction (MI) at 3 years.

RESULTS

We studied 381 patients (mean age 61 years, 21% female, 8% Killip class III/IV). Metrnl levels were associated with age, cardiovascular risk factors and the extent of coronary artery disease, as well as with STEMI complications, particularly heart failure and cardiogenic shock. Multivariable Cox regression analysis revealed that Metrnl independently predicted all-cause death or nonfatal MI at 3 years (HR, 1.86; 95%CI, 1.23-2.81; P=.003). Moreover, patients in the highest tertile (> 491.6 pg/mL) were at higher risk for the composite endpoint than those in the lowest tertiles (HR, 3.24; 95%CI, 1.92-5.44; P <.001), even after adjustment by age, diabetes mellitus, cardiac arrest, Killip-Kimball III/IV class, left ventricular ejection fraction, and creatinine clearance (HR, 1.90; 95%CI, 1.10-3.29; P=.021).

CONCLUSIONS

Circulating Metrnl levels are associated with complications during the acute phase of STEMI and independently predict a worse outcome in these patients.

Utility of Measuring Circulating Bio-Adrenomedullin and Proenkephalin for 30-Day Mortality Risk Prediction in Patients with COVID-19 and Non-COVID-19 Interstitial Pneumonia in the Emergency Department

Background and Objectives: In order to accelerate the risk stratification of patients referred to the Emergency Department (ED) with interstitial pneumonia, it could be useful to provide new and effective laboratory tests for use. The aim of our study was to evaluate the prognostic role of two biomarkers, bio-adrenomedullin (Bio-ADM) and proenkephalin (penKid), in patients with interstitial pneumonia (IP) at ED admission. Materials and Methods: In 153 consecutive patients with IP, both from COVID-19 or non-COVID-19 etiology, we measured, in a prospective observational manner, penKid and Bio-ADM at ED admission and after 24 h. In order to evaluate patient outcomes, 30-day follow-ups were also performed. The endpoints were 24 h, 10-day, and 30-day mortality. Results: Both biomarkers were shown to be good predictors of adverse events at 30 days, with Bio-ADM outperforming penKid. Bio-ADM was linked with 24 h and 10-day patient mortality. Moreover, PenKid was related to parameters defining worsening kidney function. Conclusions: Both in patients with COVID-19 or non-COVID-19 interstitial pneumonia at ED admission, Bio-ADM and penKid were good predictors of patient mortality. To evaluate these two biomarkers could be considered to be useful during the first evaluation in the ED when integrated with clinical scores.

Proenkephalin Compared to Conventional Methods to Assess Kidney Function in Critically Ill Sepsis Patients

BACKGROUND

The assessment of renal function in clinical practice remains challenging. Using creatinine to assess the glomerular filtration rate (GFR) is notoriously inaccurate, and determination of the true GFR, e.g., using inulin or iohexol, is laborious and not feasible in daily practice. Proenkephalin (PENK) is a novel candidate biomarker for kidney function that is filtrated in the glomerulus, has shown to represent steady-state GFR in patients with different severities of renal insufficiency. In this pilot study in non-steady-state critically ill patients, we compared plasma PENK concentrations with creatinine-based GFR assessments and validated both against the "true GFR" measured using a gold standard method: iohexol plasma clearance.

METHODS

Twenty-three critically ill patients with septic shock were included. Kidney function was determined using the Modification of Diet in Renal Disease formula (eGFRMDRD), Endogenous Creatinine Clearance (GFRECC), and iohexol plasma clearance (GFRiohexol) during a 6-h window. Plasma PENK concentrations were measured using the penKid immunoassay.

RESULTS

The eGFRMDRD and GFRECC correlated with the GFRiohexol (R = 0.82, P < 0.0001 and R = 0.82, P < 0.0001 respectively); however, bias and variability were considerable: the eGFRMDRD overestimated the true GFR with 31 ± 35% (95% limits of agreement: -37% to 100%) and the GFRECC with 37 ± 49% (95% limits of agreement: -59% to 133%). Plasma PENK concentrations showed a very strong inverse correlation with the GFRiohexol (R = 0.90, P < 0.0001) which tended to be better compared with the correlation of eGFRMDRD (P = 0.06) and GFRECC (P = 0.08) with the GFRiohexol.

CONCLUSIONS

In this pilot study in non-steady-state critically ill sepsis patients, GFR appears to be more accurately reflected by plasma PENK concentrations compared to conventional creatinine-based methods. Therefore, PENK holds promise as an accurate and feasible biomarker to determine kidney function during non-steady-state conditions in the critically ill.

Association of Different Estimates of Renal Function With Cardiovascular Mortality and Bleeding in Atrial Fibrillation

Background

We compared different methods of estimated glomerular filtration rate (eGFR) and their association with cardiovascular death and major bleeding in 14 980 patients with atrial fibrillation in the ARISTOTLE (Apixaban for Reduction in Stroke and Other Thromboembolic Events in Atrial Fibrillation) trial.

Methods and Results

eGFR was calculated using equations based on creatinine (Cockcroft‐Gault, Modification of Diet in Renal Disease, and Chronic Kidney Disease Epidemiology Collaboration [CKD‐EPI]) and/or cystatin C (CKD‐EPI_CysC and CKD‐EPI_{CysC+Creatinine}). These 5 eGFR equations, as well as the individual variables that are used in these equations, were assessed for correlation and discriminatory ability for cardiovascular death and major bleeding. The median age was 70.0 years, and 35.6% were women. The median eGFR was highest with Cockcroft‐Gault (74.1 mL/min) and CKD‐EPI_CysC (74.2 mL/min), and lowest with Modification of Diet in Renal Disease (66.5 mL/min). Correlation between methods ranged from 0.49 (Cockroft‐Gault and CKD‐EPI_CysC) to 0.99 (Modification of Diet in Renal Disease and CKD‐EPI). Among the eGFR equations, those based on cystatin C yielded the highest C indices for cardiovascular death and major bleeding: 0.628 (CKD‐EPI_CysC) and 0.612 (CKD‐EPI_{CysC+Creatinine}), respectively. A model based on the variables within the different eGFR equations (age, sex, weight, creatinine, and cystatin C) yielded the highest discriminatory value for both outcomes, with a C index of 0.673 and 0.656, respectively.

Conclusions

In patients with atrial fibrillation on anticoagulation, correlation between eGFR calculated using different methods varied substantially. Cystatin C–based eGFRs seem to provide the most robust information for predicting death and bleeding. A model based on the individual variables within the eGFR equations, however, provided the highest discriminatory value. Our findings may help refine risk stratification in patients with atrial fibrillation and define how renal function should be determined in future atrial fibrillation studies.

Registration

URL: https://www.clini​caltr​ials.gov; Unique identifier: NCT00412984.

Natriuretic peptides for heart failure screening in nursing homes: a systematic review

The high burden of heart failure in nursing-home populations is due to advanced age and comorbidities. Heart failure is often undiagnosed or misdiagnosed in this population and therefore remains untreated. We review the use of natriuretic peptide biomarkers for screening heart failure in nursing-home residents. The study was performed in accordance with recommendations from the Cochrane Collaboration using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses statement (PRISMA) and is registered in PROSPERO Register of Systematic Reviews. Databases PubMed, Embase, and Trip were searched from 2000 to March 2019, supplemented by hand-searching of references. Studies investigating the nursing-home population were included. The prevalence of heart failure among nursing-home residents was higher than in the general population of comparable age (23% vs 10%, respectively). The rate of misdiagnosis in nursing homes ranged from 25 to 76%. NT-proBNP was the most commonly used natriuretic peptide biomarker for heart failure screening. The mean value of NT-proBNP was significantly higher in residents with heart failure than in residents overall (pooled means of 2409 pg/mL vs 1074 pg/mL, respectively). In comparison with current guidelines, the proposed cut-off values for ruling out heart failure were higher in the analyzed studies, with ranges of 230-760 pg/mL for NT-proBNP and 50-115 pg/mL for BNP. NT-proBNP and BNP are used for screening heart failure in the nursing-home population. The current screening cut-off values are probably too low for use in nursing homes. Our most conservative estimation for ruling out heart failure is an NT-proBNP cut-off value of 230 pg/mL.

Biomarkers of Atrial Fibrillation in Metabolic Syndrome

Whether the increased atrial fibrillation (AF) risk in metabolic syndrome (MetS) patients is due to the syndrome as a whole or simply the sum of the risks of its individual component parts is still obscure. These two clinical entities share many pathophysiological links and thus distinction between a casual observation and a significant association is difficult. Biomarkers associated with pathogenesis of AF in the context of MetS have the ability to refine future risk prediction. In the present review we identify circulating substances that could be regarded as potential biomarkers for prediction of incident AF, or of cardiovascular events in the setting of AF in patients with MetS. Cardiac myocyte injury and stress markers (troponin and natriuretic peptides), markers of renal function (glomeral filtration rate, cystatin-C), and inflammation markers/mediators (interleukin- 6, CRP) are promising biomarkers of patients with AF and MetS.

Acute-phase dynamics and prognostic value of growth differentiation factor-15 in ST-elevation myocardial infarction

Background

Growth differentiation factor 15 (GDF-15) in ST-elevation myocardial infarction (STEMI) is prognostic in first-generation radioimmunoassays. We examined GDF-15 temporal dynamics in STEMI and its predictive value using a first fully automated GDF-15 electrochemiluminescence assay.

Methods

In this prospective study, circulating GDF-15 concentration was measured at admission (0 h), 12 h and 24 h in 1026 consecutive STEMI patients treated between February 2011 and May 2016 with primary percutaneous coronary intervention. GDF-15 dynamics (0 h, 12 h, 24 h) and predictive value (30 days and 3 years) were examined.

Results

Median GDF-15 concentration was 1443 pg/mL at 0 h, 1731 pg/mL at 12 h and 1510 pg/mL at 24 h (p<0.001). During follow-up, 94 patients died (9.2%) and 154 (15.0%) were hospitalized. GDF-15 was a strong predictor of 30-day mortality (hazard ratio [HR] 1.76, 95% confidence interval [CI], 1.33–2.34 at 0 h; HR 2.99 [95% CI, 2.18–4.09] at 12 h, and HR 1.97 [95% CI, 1.47–2.63] at 24 h) in multivariable Cox proportional hazards models. GDF-15 improved discrimination and reclassification of a clinical risk model. GDF-15 was also associated with 3-year mortality (HR 1.31 [95% CI, 1.04–1.65] at 0 h, HR 1.42 [95% CI, 1.10–1.84] at 12 h, and HR 1.51 [95% CI, 1.16–1.96] at 24 h) and 3-year composite of mortality and cardiovascular hospitalization (HR 1.17 [95% CI, 1.01–1.37] at 0 h, HR 1.20 [95% CI, 1.02–1.42] at 12 h, and HR 1.27 [95% CI, 1.08–1.50] at 24 h).

Conclusions

GDF-15 peaked at 12 h and remained elevated at 24 h in STEMI. GDF-15 measurement during the first 24 h in STEMI is valuable for predicting especially short- but also long-term outcomes, and may be a useful addition to risk stratification.

Repeated Measurements of Cardiac Biomarkers in Atrial Fibrillation and Validation of the ABC Stroke Score Over Time

BACKGROUND

Cardiac biomarkers are independent risk markers in atrial fibrillation, and the novel biomarker-based ABC stroke score (age, biomarkers, and clinical history of prior stroke) was recently shown to improve the prediction of stroke risk in patients with atrial fibrillation. Our aim was to investigate the short-term variability of the cardiac biomarkers and evaluate whether the ABC stroke risk score provides a stable short-term risk estimate.

METHODS AND RESULTS

According to the study protocol, samples were obtained at entry and also at 2 months in 4796 patients with atrial fibrillation followed for a median of 1.8 years in the ARISTOTLE (Apixaban for Reduction in Stroke and Other Thromboembolic Events in Atrial Fibrillation) trial. Cardiac troponin I, cardiac troponin T, and N-terminal pro-B-type natriuretic peptide were measured with high-sensitivity immunoassays. Associations with outcomes were evaluated by Cox regression. C indices and calibration plots were used to evaluate the ABC stroke score at 2 months. The average changes in biomarker levels during 2 months were small (median change cardiac troponin T +2.8%, troponin I +2.0%, and N-terminal pro-B-type natriuretic peptide +13.5%) and within-subject correlation was high (all ≥0.82). Repeated measurement of cardiac biomarkers provided some incremental prognostic value for mortality but not for stroke when combined with clinical risk factors and baseline levels of the biomarkers. Based on 8702 person-years of follow-up and 96 stroke/systemic embolic events, the ABC stroke score at 2 months achieved a similar C index of 0.70 (95% CI, 0.65-0.76) as compared with 0.70 (95% CI, 0.65-0.75) at baseline. The ABC stroke score remained well calibrated using predefined risk classes.

CONCLUSIONS

In patients with stable atrial fibrillation, the variability of the cardiac biomarkers and the biomarker-based ABC stroke score during 2 months are small. The prognostic information by the ABC stroke score remains consistent and well calibrated with similar good predictive performance if patients are retested after 2 months.

CLINICAL TRIAL REGISTRATION

URL: http://www.clinicaltrials.gov. Unique identifier: NCT00412984.

High-Sensitivity Cardiac Troponin I Is a Strong Predictor of Cardiovascular Events and Mortality in the AGES-Reykjavik Community-Based Cohort of Older Individuals

BACKGROUND

The objective of this study was to investigate the predictive power of a high-sensitivity cardiac troponin I (hs-cTnI) assay for cardiovascular events and mortality in a large population of older community dwellers.

METHODS

Blood was collected from 5764 individuals (age 66-98 years) during the period of 2002-2006 and the outcome as to all-cause death and incidence of cardiovascular disease (CVD) and coronary heart disease (CHD) followed up to 10 years. hs-cTnI (Abbott) was measured in serum to assess the association of this marker with CVD, CHD and death, and finally, to compare the results with conventional risk factors by multivariable statistical analysis.

RESULTS

The median (interquartile range) concentrations of hs-cTnI were 8.4 ng/L (5.6-14.2 ng/L) and 5.3 ng/L (3.8-8.1 ng/L) in men (2416) and women (3275), respectively, and the concentrations increased linearly with age. Outcomes as to all-cause death and incidence of CVD and CHD were significantly associated with increasing concentrations of hs-cTnI beginning well below the 99th percentile concentrations. The associations with outcome remained after adjustments for conventional risk factors and were similar in men and women.

CONCLUSIONS

Our findings suggest that hs-cTnI reflects the status of the myocardium even in seemingly healthy individuals and that the measurements of hs-cTnI may be useful for primary prediction of heart disease; this should form the basis for future prospective clinical trials for determining whether measuring hs-cTnI can be used in the prevention of CVD/CHD.

Biomarkers for risk stratification of patients with ST-elevation myocardial infarction treated with primary percutaneous coronary intervention: Insights from the Platelet Inhibition and Patient Outcomes trial

BACKGROUND

The incremental prognostic value of admission measurements of biomarkers beyond clinical characteristics and extent of coronary artery disease (CAD) in patients treated with primary percutaneous coronary intervention (PPCI) for ST-elevation myocardial infarction (STEMI) is unclear.

METHODS

Centrally analyzed plasma for biomarker measurements was available in 5,385 of the STEMI patients treated with PPCI in the PLATO trial. Extent of CAD was graded by operators in association with PPCI. We evaluated the prognostic value of high-sensitivity cardiac troponin T, N-terminal pro-B-type natriuretic peptide (NT-proBNP), and growth differentiation factor 15 (GDF-15) beyond clinical characteristics and extent of CAD using Cox proportional hazards analyses, C-index, and net reclassification improvement (NRI). Outcomes were cardiovascular death (CVD) and spontaneous myocardial infarction (MI).

RESULTS

Angiographic data on extent of CAD improved the prediction of CVD compared to clinical risk factors alone, increasing the C-index from 0.760 to 0.778, total NRI of 0.31. Biomarker information provided additional prognostic value for CVD beyond clinical risk factors and extent of CAD, C-indices ranging from 0.792 to 0.795 for all biomarkers, but with a higher NRI for NT-proBNP. Extent of CAD and high-sensitivity cardiac troponin T were not associated with spontaneous MI. The prediction of spontaneous MI beyond clinical characteristics and extent of CAD (C-index 0.647) was improved by both NT-proBNP (C-index 0.663, NRI 0.22) and GDF-15 (C-index 0.652, NRI 0.05).

CONCLUSIONS

Biomarker measurement on admission is feasible and provides incremental risk stratification in patients with STEMI treated with PPCI, with NT-proBNP and GDF-15 being most valuable due to the association with both CVD and spontaneous MI.

Two-hour diagnostic algorithms for early assessment of patients with acute chest pain--Implications of lowering the cardiac troponin I cut-off to the 97.5th percentile

AIMS

Assessment of patients with suspected non-ST elevation myocardial infarction (NSTEMI) is based on cardiac troponin (cTn) levels with the 99th percentile as cut-off. However, cardiovascular risk starts already at lower troponin concentrations. We therefore, aimed to investigate the utility of 2-hour algorithms using the high-sensitivity cardiac troponin I (hs-cTnI) 97.5th percentile as cut-off which corresponds to the standard URL for most biomarkers.

METHODS

Hs-cTnI was measured at presentation and 2h in 1624 chest pain patients. Diagnostic algorithms were developed applying hs-cTnI levels dichotomized at the 99th and 97.5th percentiles combined with hs-cTnI changes and/or ECG findings.

RESULTS

The prevalence of NSTEMI was 13.9%. The adjusted odds ratios for 1-year mortality were 2.7 (95% CI 1.4-5.1) for the 99th percentile and 3.1 (95% CI 1.6-5.9) for the 97.5th percentile. The best-performing 99th percentile-based algorithms provided a positive predictive value (PPV) of 86.3% and a negative predictive value (NPV) of 99.3%. Using 97.5th percentile-based algorithms to define NSTEMI resulted in few reclassifications and yielded similar diagnostic estimates (PPV 85.4%, NPV 99.4%).

CONCLUSION

The hs-cTnI 97.5th percentile integrated into 2-hour algorithms provided high diagnostic estimates and could, due to better prognostic properties serve as an alternative to the 99th percentile.

Cardiac troponin I levels in patients with non-ST-elevation acute coronary syndrome-the importance of gender

BACKGROUND

Measurement of high-sensitivity cardiac troponin levels is increasingly used in non-ST-elevation acute coronary syndrome (NSTE-ACS). However, studies investigating the distribution and prognostic implications of high-sensitivity troponin levels in men and women separately are currently lacking.

METHODS

Cardiac troponin I (cTnI) levels were determined using a high-sensitivity assay (Abbott Laboratories, Abbott Park, IL) in 1,677 male and 1,073 female NSTE-ACS patients participating in the GUSTO IV study. The prognostic associations of cTnI to outcome (30-day composite end point of recurrent myocardial infarction and 1-year mortality) were assessed in multivariable models, using cTnI both as a continuous variable and dichotomized at different sets of single and gender-specific 99th percentiles.

RESULTS

Median cTnI levels were 947 and 175 ng/L in men and women, respectively (P < .001). The adjusted odds ratios for cTnI (ln) were similar in men and women. The adjusted odds ratios for cTnI above the tested 99th percentiles levels in contrast were twice as high in women compared with men. This was a consequence of differences in the cTnI distribution and risk gradients across cTnI levels, in particular due to lower event rates in women without cTnI elevation. Gender-specific cutoffs did not improve risk prediction.

CONCLUSIONS

Despite overall lower levels, cTnI above the tested 99th percentiles exhibited stronger prognostic information in women with NSTE-ACS compared with men. This likely reflects differences in the pathophysiology and the clinical presentation in NSTE-ACS. Our data, thus, emphasize that women with symptoms of unstable coronary artery disease encompass a broader risk panorama than men.

Importance of persistent elevation of cardiac biomarkers in atrial fibrillation: a RE-LY substudy

OBJECTIVES

To evaluate the prognostic importance of transient or persistent elevations of cardiac troponin-I (cTnI) and N-terminal-B-type natriuretic peptide (NT-proBNP) in atrial fibrillation (AF).

METHODS

Plasma samples were obtained at randomisation and after 3 months in 2514 patients with AF in the RE-LY trial; median follow-up was 2.0 years. Patients were grouped based on levels at the two time points according to detectable cTnI levels (≥0.01 µg/L) or NT-proBNP levels above median (≥778 ng/L). These groups were related to occurrence of stroke or cardiovascular events evaluated with Cox models adjusting for established risk factors.

RESULTS

The proportion of patients with detectable cTnI levels at both time points was 48.5%, at one time point 28.5% and at neither time point 21.0%. Patients with detectable cTnI at both time points had substantially higher rates of stroke compared with those with transient elevations and those with no elevation at either time point (p<0.005, effect of cTnI). Persistent elevation of either or both cardiac biomarkers at baseline and 3 months was associated with a higher risk for cardiovascular events and mortality (p<0.0001). Prognostic prediction improved most with the use of repeated measurements of both cardiac biomarkers simultaneously (p<0.05) and achieved C-statistic 0.644 for stroke compared with 0.611 for CHADS2-score.

CONCLUSIONS

Persistent elevation of troponin and NT-proBNP indicates a worse prognosis than transient elevations or no elevations of either marker. Prognostication of stroke, death and thromboembolic events is improved by the use of repeated determinations of cardiac biomarkers.

TRIAL REGISTRATION NUMBER

http://www.clinicaltrials.gov, NCT00262600.

Short- and long-term individual variation in NT-proBNP levels in patients with stable coronary artery disease

BACKGROUND

In addition to diagnosis of heart failure (HF) natriuretic peptides (BNP and NT-proBNP) may be used for risk prediction in stable and acute coronary artery disease. The aim of the study was to evaluate the short- and long-term individual variation of NT-proBNP in patients with stable coronary artery disease.

METHODS

Twenty-four patients with suspected stable coronary artery disease and scheduled for elective coronary angiography were included. Blood samples were drawn at enrolment and, on average 3 weeks later, serially the day prior to coronary angiography. NT-proBNP was determined using Elecsys proBNP sandwich immunoassay (Roche Diagnostics).

RESULTS

The individual variation in NT-proBNP over 4h was 11.8%, over 20 h 12.4% and over 3 weeks 20.4%. The corresponding positive and negative lognormal reference change values (RCV) were +41/-29%, +42/-30% and +76/-43%, respectively. No significant circadian variation was found.

CONCLUSIONS

Our results suggest that an increase in NT-proBNP levels of >42% or a decrease of >30% is needed to indicate a reliable short-term change; and for a long-term change an increase of >76% or a decrease of >43% is required. This should be considered when interpreting changes in NT-proBNP levels.

N-terminal pro-B-type natriuretic peptide for risk assessment in patients with atrial fibrillation: insights from the ARISTOTLE Trial (Apixaban for the Prevention of Stroke in Subjects With Atrial Fibrillation)

OBJECTIVES

This study sought to assess the prognostic value of N-terminal pro-B-type natriuretic peptide (NT-proBNP) in patients with atrial fibrillation (AF) enrolled in the ARISTOTLE (Apixaban for the Prevention of Stroke in Subjects With Atrial Fibrillation) trial, and the treatment effect of apixaban according to NT-proBNP levels.

BACKGROUND

Natriuretic peptides are associated with mortality and cardiovascular events in several cardiac diseases.

METHODS

In the ARISTOTLE trial, 18,201 patients with AF were randomized to apixaban or warfarin. Plasma samples at randomization were available from 14,892 patients. The association between NT-proBNP concentrations and clinical outcomes was evaluated using Cox proportional hazard models, after adjusting for established cardiovascular risk factors.

RESULTS

Quartiles of NT-proBNP were: Q1, ≤363 ng/l; Q2, 364 to 713 ng/l; Q3, 714 to 1,250 ng/l; and Q4, >1,250 ng/l. During 1.9 years, the annual rates of stroke or systemic embolism ranged from 0.74% in the bottom NT-proBNP quartile to 2.21% in the top quartile, an adjusted hazard ratio of 2.35 (95% confidence interval [CI]: 1.62 to 3.40; p < 0.0001). Annual rates of cardiac death ranged from 0.86% in Q1 to 4.14% in Q4, with an adjusted hazard ratio of 2.50 (95% CI: 1.81 to 3.45; p < 0.0001). Adding NT-proBNP levels to the CHA2DS2VASc score improved C-statistics from 0.62 to 0.65 (p = 0.0009) for stroke or systemic embolism and from 0.59 to 0.69 for cardiac death (p < 0.0001). Apixaban reduced stroke, mortality, and bleeding regardless of the NT-proBNP level.

CONCLUSIONS

NT-proBNP levels are often elevated in AF and independently associated with an increased risk of stroke and mortality. NT-proBNP improves risk stratification beyond the CHA2DS2VASc score and might be a novel tool for improved stroke prediction in AF. The efficacy of apixaban compared with warfarin is independent of the NT-proBNP level. (Apixaban for the Prevention of Stroke in Subjects With Atrial Fibrillation [ARISTOTLE]; NCT00412984).

Biomarkers in atrial fibrillation: a clinical review

Assessment of atrial fibrillation (AF)-associated stroke risk is at present mainly based on clinical risk scores such as CHADS2 and CHA2DS2-VASc, although these scores provide only modest discrimination of risk for individual patients. Biomarkers derived from the blood may help refine risk assessment in AF for stroke outcomes and for mortality. Recent studies of biomarkers in AF have shown that they can substantially improve risk stratification. Cardiac biomarkers, such as troponin and natriuretic peptides, significantly improve risk stratification in addition to current clinical risk stratification models. Similar findings have recently been described for markers of renal function, coagulation, and inflammation in AF populations based on large randomized prospective clinical trials or large community-based cohorts. These new findings may enable development of novel tools to improve clinical risk assessment in AF. Biomarkers in AF may also improve the understanding of the pathophysiology of AF further as well as potentially elucidate novel treatment targets. This review will highlight novel associations of biomarkers and outcomes in AF as well as recent progress in the use of biomarkers for risk stratification.

Efficacy of apixaban when compared with warfarin in relation to renal function in patients with atrial fibrillation: insights from the ARISTOTLE trial

AIMS

Atrial fibrillation (AF) is common among patients with impaired renal function. Apixaban, a novel oral anticoagulant with partial renal excretion, was compared with warfarin and reduced the rate stroke, death and bleeding in the ARISTOTLE trial. We evaluated these outcomes in relation to renal function.

METHODS AND RESULTS

Baseline glomerular filtration rate (GFR) was estimated using the Cockcroft-Gault and Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equations as well as cystatin C measurements. According to baseline Cockcroft-Gault, there were 7518 patients (42%) with an estimated GFR (eGFR) of >80 mL/min, 7587 (42%) between >50 and 80 mL/min, and 3017 (15%) with an eGFR of ≤50 mL/min. The rate of cardiovascular events and bleeding was higher at impaired renal function (≤80 mL/min). Apixaban was more effective than warfarin in preventing stroke or systemic embolism and reducing mortality irrespective of renal function. These results were consistent, regardless of methods for GFR estimation. Apixaban was associated with less major bleeding events across all ranges of eGFRs. The relative risk reduction in major bleeding was greater in patients with an eGFR of ≤50 mL/min using Cockcroft-Gault {hazard ratio (HR) 0.50 [95% confidence interval (CI) 0.38-0.66], interaction P = 0.005} or CKD-EPI equations [HR 0.48 (95% CI 0.37-0.64), interaction P = 0.003].

CONCLUSION

In patients with AF, renal impairment was associated with increased risk of cardiovascular events and bleeding. When compared with warfarin, apixaban treatment reduced the rate of stroke, death, and major bleeding, regardless of renal function. Patients with impaired renal function seemed to have the greatest reduction in major bleeding with apixaban.

Predicting the Risk of Cardiovascular Disease

Although an atherogenic lipoprotein phenotype has been well recognized as an important predictor of cardiovascular disease, recent studies have demonstrated a number of additional lipid-related markers as emerging biomarkers to identify patients at risk for future coronary heart disease. Among them, lipoprotein-associated phospholipase A(2) (Lp-PLA(2)), seems to be a promising candidate that might be added to the clinical armamentarium for improved prediction of cardiovascular disease in the future. Of particular note, Lp-PLA(2) is the only enzyme that cleaves oxidized low-density lipoprotein (oxLDL) in the subendothelial space, with further generation of proinflammatory mediators such as lysophosphatidylcholine (LysoPC) and oxidized fatty acid (oxFA), thereby probably linking two important features of atherogenesis, namely oxidation of LDL and local inflammatory processes within the atherosclerotic plaque. This overview aims to summarize our current knowledge based on observations from recent experimental and clinical studies. Emphasis has been put on potential pathophysiological mechanisms of action and on the clinical relevance of Lp-PLA(2) in a wide variety of clinical settings, including apparently healthy individuals, patients with stable angina or acute coronary syndromes, after myocardial infarction, and with subclinical disease. Although a growing body of evidence from epidemiological and clinical studies suggests that Lp-PLA(2) may represent an independent and clinically relevant long-term risk marker for coronary heart disease and, probably, also for stroke, the role of this enzyme in the setting of the acute coronary syndrome remains to be established.

Cardiac biomarkers are associated with an increased risk of stroke and death in patients with atrial fibrillation: a Randomized Evaluation of Long-term Anticoagulation Therapy (RE-LY) substudy

BACKGROUND

Cardiac biomarkers are strong predictors of adverse outcomes in several patient populations. We evaluated the prevalence of elevated troponin I and N-terminal pro-B-type natriuretic peptide (NT-proBNP) and their association to cardiovascular events in atrial fibrillation (AF) patients in the Randomized Evaluation of Long-Term Anticoagulation Therapy (RE-LY) trial.

METHODS AND RESULTS

Biomarkers at randomization were analyzed in 6189 patients. Outcomes were evaluated by Cox proportional hazards models adjusting for established cardiovascular risk factors and the CHADS(2) and CHA(2)DS(2)-VASc risk scores. Patients were stratified based on troponin I concentrations: <0.010 μg/L, n=2663; 0.010 to 0.019 μg/L, n=2006; 0.020 to 0.039 μg/L, n=1023; ≥0.040 μg/L, n=497; and on NT-proBNP concentration quartiles: <387; 387 to 800; 801 to 1402; >1402 ng/L. Rates of stroke were independently related to levels of troponin I with 2.09%/year in the highest and 0.84%/year in the lowest troponin I group (hazard ratio [HR], 1.99 [95% CI, 1.17-3.39]; P=0.0040), and to NT-proBNP with 2.30%/year versus 0.92% in the highest versus lowest NT-proBNP quartile groups, (HR, 2.40 [95% CI, 1.41-4.07]; P=0.0014). Vascular mortality was also independently related to biomarker levels with 6.56%/year in the highest and 1.04%/year the lowest troponin I group (HR, 4.38 [95% CI, 3.05-6.29]; P<0.0001), and 5.00%/year in the highest and 0.61%/year in the lowest NT-proBNP quartile groups (HR, 6.73 [3.95-11.49]; P<0.0001). Biomarkers increased the C-statistic from 0.68 to 0.72, P<0.0001, for a composite of thromboembolic events.

CONCLUSIONS

Elevations of troponin I and NT-proBNP are common in patients with AF and independently related to increased risks of stroke and mortality. Cardiac biomarkers seem useful for improving risk prediction in AF beyond currently used clinical variables.

ProteinSeq: high-performance proteomic analyses by proximity ligation and next generation sequencing

Despite intense interest, methods that provide enhanced sensitivity and specificity in parallel measurements of candidate protein biomarkers in numerous samples have been lacking. We present herein a multiplex proximity ligation assay with readout via realtime PCR or DNA sequencing (ProteinSeq). We demonstrate improved sensitivity over conventional sandwich assays for simultaneous analysis of sets of 35 proteins in 5 µl of blood plasma. Importantly, we observe a minimal tendency to increased background with multiplexing, compared to a sandwich assay, suggesting that higher levels of multiplexing are possible. We used ProteinSeq to analyze proteins in plasma samples from cardiovascular disease (CVD) patient cohorts and matched controls. Three proteins, namely P-selectin, Cystatin-B and Kallikrein-6, were identified as putative diagnostic biomarkers for CVD. The latter two have not been previously reported in the literature and their potential roles must be validated in larger patient cohorts. We conclude that ProteinSeq is promising for screening large numbers of proteins and samples while the technology can provide a much-needed platform for validation of diagnostic markers in biobank samples and in clinical use.

Natriuretic peptides: ready for prime-time in hypertension?

Over the past years, natriuretic peptides have been recognised not only as important contributors to cardiovascular regulation but also as valuable markers in overt cardiac disease, including heart failure or coronary disease. More recently, these markers have shown their ability to detect preclinical cardiac alterations in different settings. In this respect, natriuretic peptides offer a new perspective for risk stratification in hypertension. They are correlated to various features of cardiac remodelling provoked by hypertension. They also depend on vascular properties, including blood pressure level and aortic stiffness. In addition to being integrative markers of cardiovascular alterations, several studies have shown their value in predicting all-cause mortality or cardiovascular mortality and morbidity in the general population. At least three consistent studies are now available in hypertension also showing this prognostic value. This performance, together with the ease of measurement, low cost and widespread availability, should prompt the wide use of natriuretic peptides for risk stratification in hypertension, at least in patients with normal electrocardiography, but also in most hypertensive patients.

N-terminal-pro-brain natriuretic peptide is decreased in insulin dependent gestational diabetes mellitus: a prospective cohort trial

Background

N-terminal-pro-brain natriuretic peptide (NT-proBNP) is elevated in gestational hypertension and preeclampsia. This trial aimed to generate data for gestational diabetes mellitus patients, who are at risk to develop these complications.

Methods

We have measured NT-proBNP in 223 otherwise healthy women between gestational week 24 and 32 referred to the outpatient diabetes unit in a cross-sectional study.

Results

88 control subjects, 45 patients with indication for medical nutrition therapy (MNT) alone and 90 patients who required insulin therapy were included. Groups of women were comparable regarding gestational week. Body mass index before pregnancy and at blood draw was significantly higher in subjects with insulin dependent gestational diabetes mellitus compared to MNT controlled gestational diabetes mellitus. NT-proBNP was significantly lower in patients with insulin dependent gestational diabetes mellitus (35 ± 25 pg/ml) compared to controls (53 ± 43 pg/ml, p = 0.012).

Conclusions

NT-proBNP is within the reference range of normal subjects in women with gestational diabetes mellitus. Differences in body mass index, changes in glomerular filtration rate and haemodynamics may explain lower NT-proBNP concentrations in insulin dependent gestational diabetes mellitus. A false negative interpretation needs to be considered in these women.

N-Terminal Pro-Brain Natriuretic Peptide

See Editorial Commentary, pp 670–671

Natriuretic peptides are controregulatory hormones associated with cardiac remodeling, namely, left ventricular hypertrophy and systolic/diastolic dysfunction. We intended to address the prognostic value of N-terminal pro-brain natriuretic peptide (NT-proBNP) in hypertension. We prospectively studied the relationship between plasma NT-proBNP and all-cause mortality in 684 hypertensive patients with no history or symptoms of heart failure referred for hypertension workup in our institution from 1998 to 2008. After a mean duration of 5.7 years, we observed 40 deaths (1.04 deaths per 100 patients per year). After adjustment for traditional cardiovascular risk factors, including ambulatory blood pressure and serum creatinine, the risk for all-cause mortality more than doubled with each increment of 1 log NT-proBNP (hazard ratio: 2.33 [95% CI: 1.36 to 3.96]). The risk of death of patients with plasma NT-proBNP ≥133 pg/mL (third tertile of the distribution) was 3.3 times that of patients with values <50.8 pg/mL (first tertile; hazard ratio: 3.30 [95% CI: 0.90 to 12.29]). This predictive value was independent of, and superior to, that of 2 ECG indexes of left ventricular hypertrophy, the Sokolov-Lyon index and the amplitude of the R wave in lead aVL. In addition, it persisted in patients without ECG left ventricular hypertrophy, which allowed refining risk stratification in this relatively low-risk patient category. In this large sample of hypertensive patients, plasma NT-proBNP appeared as a strong prognostic marker. This performance, together with the ease of measurement, low cost, and widespread availability of NT-proBNP test kits, should prompt a wide use of this marker for risk stratification in hypertension.

The relationship of cystatin C, creatinine, estimated GFR, and cardiovascular events

This study examined the predictive value of plasma cystatin C, creatinine and estimated glomerular filtration rate (eGFR) as risk factors for cardiovascular disease in Chinese. Plasma cystatin C and creatinine were measured in 466 coronary heart disease (CHD) patients recruited from 4 hospitals and 349 healthy controls from local communities in Wuhan, China. Cockroft-Gault formula was used to estimate the glomerular filtration rate (GFR) after adjusting for body surface area. With each measure, the study population was divided into quintiles. The results showed that the patients had significantly higher levels of plasma cystatin C, creatinine, and lower level of eGFR than controls. Lower eGFR was associated with a higher risk of cardiovascular events. As compared with the first (highest) quintile, the hazard ratios (and 95% CIs) after multivariate adjustment for CHD were as follows: third quintile, 2.98 (1.54-5.78); fourth quintile, 3.34 (1.58-7.09); fifth quintile, 4.37(1.84-10.35). With higher cystatin C quintiles (≥1.00 mg/L and ≥1.17 mg/L), the hazard ratios for CHD were 2.16 (1.23-3.81) and 2.34 (1.25-4.38), similar to those of creatinine 2.21 (1.21-4.03) and 2.03 (1.07-3.84). However, it was plasma cystatin C not eGFR or creatinine had stronger association with ischemic stroke. The highest quintile had the hazard ratio of 4.51 (1.45-14.08) after multivariate adjustment. It was concluded that plasma cystatin C, associated with renal function, is not an independent risk factor for cardiovascular disease. eGFR is a better risk predictor for CHD than plasma cystatin C and creatinine. But for ischemic stroke, plasma cystatin C is a better risk factor than creatinine and estimated GFR.

Niemann-Pick C1 modulates hepatic triglyceride metabolism and its genetic variation contributes to serum triglyceride levels

OBJECTIVE

To study how Niemann-Pick disease type C1 (NPC1) influences hepatic triacylglycerol (TG) metabolism and to determine whether this is reflected in circulating lipid levels.

METHODS AND RESULTS

In Npc1(-/-) mice, the hepatic cholesterol content is increased but the TG content is decreased. We investigated lipid metabolism in Npc1(-/-) mouse hepatocytes and the association of NPC1 single-nucleotide polymorphisms with circulating TGs in humans. TGs were reduced in Npc1(-/-) mouse serum and hepatocytes. In Npc1(-/-) hepatocytes, the incorporation of [3H]oleic acid and [3H]acetate into TG was decreased, but shunting of oleic acid- or acetate-derived [3H]carbons into cholesterol was increased. Inhibition of cholesterol synthesis normalized TG synthesis, content, and secretion in Npc1(-/-) hepatocytes, suggesting increased hepatic cholesterol neogenesis as a cause for the reduced TG content and secretion. We found a significant association between serum TG levels and 5 common NPC1 single-nucleotide polymorphisms in a cohort of 1053 men, with the lowest P=8.7 x 10(-4) for the single-nucleotide polymorphism rs1429934. The association between the rs1429934 A allele and higher TG levels was replicated in 2 additional cohorts, which included 8041 individuals.

CONCLUSIONS

This study provides evidence of the following: (1) in mice, loss of NPC1 function reduces hepatocyte TG content and secretion by increasing the metabolic flux of carbons into cholesterol synthesis; and (2) common variation in NPC1 contributes to serum TG levels in humans.

NT-proBNP levels in systemic sclerosis: association with clinical and laboratory abnormalities

OBJECTIVE

To identify factors related to NT-proBNP levels in systemic sclerosis (SSc).

DESIGN AND METHODS

NT-proBNP was measured in 119 patients with SSc and 20 controls. Patients with transtricuspid gradient (TG) > or =36 mm Hg or > or =31 mmHg plus dyspnea were considered to have suspected systemic sclerosis-associated pulmonary arterial hypertension (SScPAH).

RESULTS

Increasing age, NYHA functional class, skin score, history of systemic arterial hypertension (SAH), anticentromere antibodies, diastolic dysfunction, reduced pulmonary diffusing capacity, and TG were positively associated with NT-proBNP. In multivariable linear regression, TG, age, and SAH were independently associated to NT-proBNP levels. An ROC curve analysis (with an area under the curve of 0.89, 95% CI: 0.83-0.95) suggested a cutoff of 157.8pg/mL to identify patients with suspected SScPAH, presenting a sensitivity of 100% (78.1-100) and specificity of 72.3% (62.3-80.5).

CONCLUSIONS

NT-proBNP levels are related to clinical and laboratory abnormalities in SSc. The results indicate that NT-proBNP may be a useful tool in the evaluation of SScPAH.

Cystatin C levels in patients with beta-thalassemia during deferasirox treatment

Deferasirox (Exjade) is a once-daily, oral iron chelator approved for the treatment of transfusional iron overload. This study was conducted to analyze changes in cystatin C concentration, an endogenous marker of glomerular filtration rate (GFR), in patients with thalassemia receiving daily deferasirox therapy over a period of at least 9 months. One hundred and fifty beta-thalassemia patients were treated with deferasirox at doses of 20-40 mg/kg/day for 9 consecutive months. Cystatin C concentrations were measured at regular intervals and GFR was calculated according to the cystatin C-based prediction equation. Plasma concentrations of NGAL protein and NT-proBNP were also monitored as indicators of renal function and LVEF, respectively. Serum ferritin concentration was also measured to assess iron overload. Throughout the 9 months of deferasirox treatment cystatin C concentration remained stable (p>0.850). The baseline cystatin C mean values were 0.97+/-0.27 mg/L and reached a maximum of 1.01+/-0.29 mg/L at 4 months of treatment. No correlation was found between cystatin C and NGAL concentrations (p>0.674). Cystatin C and NT-proBNP concentrations correlated positively with a binomial equation (p<0.004), as also did cystatin C and serum ferritin (p<0.001). These findings suggest that slight changes of cystatin C during deferasirox treatment may not reflect renal injury. However hemodynamic signals such as LVEF alterations and iron mobilization do appear to affect changes in cystatin C concentration.

Predisposing factors and consequences of elevated biomarker levels in long-distance runners aged >or=55 years

Cardiac biomarkers play an important role in the diagnosis of cardiovascular disease. Elevated levels can be seen in the context of strenuous exercise. We studied this phenomenon in senior endurance runners. We included 185 participants (61.1 +/- 5 years; 29% women) at a 30-km cross-country race who were self-reportedly in excellent health. Before and after the race, the creatinine, N-terminal pro-brain natriuretic peptide (NT-proBNP), and troponin T were analyzed, and participation in the number of previous races and the race duration were recorded. NT-proBNP increased from 53 ng/L (interquartile range 31 to 89) to 121 ng/L (interquartile range 79 to 184) and troponin T from undetectable to 0.01 microg/L (interquartile range 0.01 to 0.04). The independent predictors of a large NT-proBNP increase were (1) greater levels present at baseline, (2) a greater increase in creatinine (both p <0.001), (3) older age (p = 0.01), and (4) a longer race duration (p <0.05). Troponin T elevation was independently predicted by (1) older age (p = 0.01), (2) a greater increase in creatinine, and (3) participation in fewer previous races (both p <0.05). Of the 15 runners with an elevated (>194 ng/L) baseline NT-proBNP level (8.1% of 185), 4 were found to have serious cardiovascular disease (2.2% of whole sample). Of these 4 patients, 1 died from sudden cardiac death within months after the race. In conclusion, biomarker elevation occurs commonly in senior runners. A high baseline NT-proBNP is predictive of a large release during exercise, suggesting that the factors that control the at rest levels also determine its release with exertion. Troponin T elevation was seen in less-experienced participants. A small group of very ill runners were identified by NT-proBNP analysis.

Baseline plasma NT-proBNP and clinical characteristics: results from the irbesartan in heart failure with preserved ejection fraction trial

BACKGROUND

N-terminal B type natriuretic peptide (NT-proBNP) is usually elevated in heart failure (HF) patients with reduced ejection fraction (EF). Less is known about NT-proBNP in HF with preserved EF (HF-PEF). We measured baseline NT-proBNP in 3562 HF-PEF enrolled patients in the Irbesartan in Heart Failure with Preserved Ejection Fraction trial.

METHODS AND RESULTS

Patients with EF >or=45%, age >or=60 years, and either New York Heart Association (NYHA) II-IV symptoms with HF hospitalization (HFH) within 6 months or NYHA III-IV symptoms with corroborative evidence of HF or structural changes associated with HF-PEF. NT-proBNP (pg/mL) measured centrally using the Elecsys proBNP assay (Roche). Mean age 72 +/- 7 years, 60% were women, the investigator indicated HF etiology was hypertension in 64%; the majority were in NYHA III. Medications included diuretics in 82%, angiotensin-converting enzyme inhibitor in 26%, beta-blocker in 59%, and spironolactone in 15%. Median NT-proBNP was 341 pg/mL (interquartile range 135 to 974 pg/mL) and geometric mean was 354 pg/mL. In multivariate analysis, the baseline characteristics most strongly associated with higher NT-proBNP levels were atrial fibrillation (ratio of geometric mean 2.59, P < .001), NYHA IV symptoms (1.52, P < .001), lower estimated glomerular filtration rate (1.44, P < .001), and HFH hospitalization within 6 months (1.37, P < .001).

CONCLUSIONS

Most HF-PEF patients have elevated NT-proBNP levels. The NT-proBNP concentrations were related to baseline characteristics generally associated with worse outcomes for HF patients.

Normal plasma levels of cardiac troponin I measured by the high-sensitivity cardiac troponin I access prototype assay and the impact on the diagnosis of myocardial ischemia

OBJECTIVES

This study sought to evaluate the analytical and clinical performance of the novel hypersensitive cardiac troponin I (cTnI) prototype assay from Beckman Coulter (Fullerton, California).

BACKGROUND

Studies on patients with acute coronary syndromes and on seemingly healthy subjects have shown that even very minor elevations of cardiac troponins are associated with an increased risk of death. However, the normal plasma levels of cardiac troponins are still not known.

METHODS

cTnI plasma levels were measured in 542 healthy subjects, 319 men (age 59.9 +/- 11.8 years) and 213 women (age 59.8 +/- 13.1 years), and in 1,503 randomly selected patients of the GUSTO IV (Global Utilization of Strategies To open Occluded arteries IV) cohort with unstable angina and non-ST-segment elevation myocardial infarctions (MIs).

RESULTS

The cTnI levels at 10% coefficient of variation and 20% coefficient of variation imprecision were 0.0033 and 0.0016 microg/l, respectively. The cTnI levels were measurable in >95% of the healthy subjects. The median level of healthy subjects <60 years of age was 0.0032 microg/l (range 0.0011 to 0.0079 microg/l) with the 99th percentile being 0.010 microg/l. No sex differences were observed. A receiver-operator characteristic curve analysis showed an optimal discrimination between healthy subjects and patients at 0.0064 microg/l with a sensitivity of 84.8% (95% confidence interval: 82.8% to 86.6%) and specificity of 89.7% (95% confidence interval: 86.8% to 92.2%). Outcomes as to death and/or MI were significantly different at this level (p < 0.01) in the GUSTO IV cohort.

CONCLUSIONS

The novel high-sensitivity cTnI prototype assay from Beckman Coulter allows for the first time the measurement of cTnI levels in almost all healthy subjects. Our data indicate that the assay may be a powerful aid in the diagnosis and outcome prediction of patients with suspected myocardial ischemia and question any definition of myocardial infarction.

Evaluation of Gentian cystatin C reagent on Abbott Ci8200 and calculation of glomerular filtration rate expressed in mL/min/1.73 m2from the cystatin C values in mg/L

OBJECTIVE

Estimation of the glomerular filtration rate (GFR) is essential when evaluating patients with kidney disease and treating patients with drugs eliminated from the circulation by the kidneys. Cystatin C has been shown in several studies to be superior to creatinine in the estimation of GFR. At our hospitals, there is an increasing demand for cystatin C and at present we perform approximately 1500 cystatin C analyses a month. We thus need the assay available 24 h/day and to have it on our routine chemistry instrument to minimize handling time per test and time to reported test results.

MATERIAL AND METHODS

We have evaluated a new cystatin C immunoassay from Gentian (Gentian, Moss, Norway) on Architect ci8200 (Abbott Laboratories, Abbott Park, Ill., USA). A prerequisite at our hospital is that cystatin C results are reported as a calculated GFR in mL/min/1.73 m(2), so we also made a comparison with iohexol clearance.

RESULTS

The Gentian cystatin C assay showed good agreement with the corresponding assay from Dade Behring (Deerfield, Ill., USA) and good inter-laboratory concordance. The assay has very low total imprecision, good linearity and strong correlation with iohexol clearance (R (2) = 0.956). The equation for the correlation curve is: y = 79.901x(-1.4389).

CONCLUSIONS

There was low inter-laboratory variation between the three laboratories involved in the cystatin C evaluation, and thus all three laboratories can use the same equation for calculating the estimated GFR.

Effect of azotemia on serum N-terminal proBNP concentration in dogs with normal cardiac function: a pilot study

OBJECTIVES

To evaluate amino-terminal pro-B type natriuretic peptide (NT-proBNP) concentration in dogs with renal dysfunction and normal cardiac structure and function.

ANIMALS

Eight dogs with renal disease, 23 healthy control dogs.

METHODS

Serum NT-proBNP concentration was measured in healthy dogs and dogs with renal disease using an ELISA validated for use in dogs. Affected dogs were eligible for inclusion if renal dysfunction was diagnosed based on urinalysis and serum chemistry, and if they were free of cardiovascular disease based on physical exam, systolic blood pressure, and echocardiography.

RESULTS

The geometric mean serum NT-proBNP concentration was significantly higher in dogs with renal disease (617 pmol/L; 95% CI, 260-1467 pmol/L) than in healthy control dogs (261 pmol/L; 95% CI, 225-303 pmol/L; P=0.0014). There was a modest positive correlation between NT-proBNP and BUN and creatinine. Median NT-proBNP concentration was not significantly different between groups when indexed to BUN (median NT-proBNP:BUN ratio; renal, 14.2, IQR, 3.93-17.7 vs. control, 16.3, IQR, 9.94-21.2; P=0.29) or creatinine (median NT-proBNP:creatinine ratio; renal, 204, IQR, 72.6-448 vs. control, 227, IQR, 179-308; P=0.67).

CONCLUSION

Dogs with renal disease had significantly higher mean serum concentration of NT-proBNP than control dogs. Renal function should be considered when interpreting NT-proBNP results as concentrations may be falsely elevated in dogs with renal dysfunction and normal cardiac function. The effect of renal disease was lessened by indexing NT-proBNP to BUN or creatinine. Future studies in dogs with both renal and heart disease are warranted.

Clinical Performance of Two Highly Sensitive Cardiac Troponin I Assays

Background: The aim of this study was to compare the clinical performance of 2 sensitive cTnI assays with 10% CV imprecision below the 99th percentile upper reference limit.

Methods: We measured cardiac troponin and N-terminal pro-brain natriuretic peptide (NT-proBNP) concentrations in a random sample of the Global Use of Strategies To Open Occluded Coronary Arteries (GUSTO) IV cohort (n = 1251). Outcome data of 1-year mortality and the composite endpoint DMI [death and/or myocardial infarction (MI) within 30 days] were available in all patients. The 99th percentile of a healthy population was estimated from the Sweden Women and Men and Ischemic Heart Disease (SWISCH) cohort (n = 442). We measured cardiac troponin I (cTnI) using the Access AccuTnI (Beckman Coulter) and Centaur TnI Ultra (Siemens Healthcare Diagnostics) and NT-proBNP using the Elecsys 2010 (Roche Diagnostics).

Results: Applying the 10% CV cutoff, the sensitivity of the Access AccuTnI assay in identifying DMI and death was higher than that of the Centaur TnI Ultra (P = 0.02 and P &lt; 0.001), and the AccuTnI assay also identified more patients at risk (P &lt; 0.001) and with poor outcome. Applying the 99th percentile cutoffs, AccuTnI identified more patients at risk than the Centaur TnI (P &lt; 0.001) and with significant differences in outcome. Significantly more patients with cardiac troponins below the cutoffs as measured by Centaur TnI had increased NT-proBNP concentrations (P &lt; 0.001) compared with AccuTnI.

Conclusions: The AccuTnI assay identified more patients at risk than the Centaur cTnI Ultra assay. Our results demonstrate the clinical potential of high-sensitivity cardiac troponin assays for the identification of patients at risk of dying from cardiovascular disease.

Biochemistry and Clinical Role of Human Cystatin C

Low molecular-mass plasma proteins play a key role in health and disease. Cystatin C is an endogenous cysteine proteinase inhibitor belonging to the type 2 cystatin superfamily. The mature, active form of human cystatin C is a single non-glycosylated polypeptide chain consisting of 120 amino acid residues, with a molecular mass of 13,343-13,359 Da, and containing four characteristic disulfide-paired cysteine residues. Human cystatin C is encoded by the CST3 gene, ubiquitously expressed at moderate levels. Cystatin C monomer is present in all human body fluids; it is preferentially abundant in cerebrospinal fluid, seminal plasma, and milk. Cystatin C L68Q variant is an amyloid fibril-forming protein with a high tendency to dimerize. It forms self-aggregates with massive amyloid deposits in the brain arteries of young adults, leading to lethal cerebral hemorrhage. The main catabolic site of cystatin C is the kidney: more than 99% of the protein is cleared from the circulation by glomerular ultrafiltration and tubular reabsorption. The diagnostic value of cystatin C as a marker of kidney dysfunction has been extensively investigated in multiple clinical studies on adults, children, and in the elderly. In almost all the clinical studies, cystatin C demonstrated a better diagnostic accuracy than serum creatinine in discriminating normal from impaired kidney function, but controversial results have been obtained by comparing this protein with other indices of kidney disease, especially serum creatinine-based equations. In this review, we present and discuss most of the available data from the literature, critically reviewing conclusions and suggestions for the use of cystatin C in clinical practice. Despite the multitude of clinical data in the literature, cystatin C has not been widely used, perhaps because of a combination of factors, such as a general diffidence among clinicians, the absence of definitive cut-off values, conflicting results in clinical studies, no clear evidence on when and how to request the test, the poor commutability of results, and no accurate examination of costs and of its routine use in a stat laboratory.

Serum cystatin C in the United States: the Third National Health and Nutrition Examination Survey (NHANES III)

BACKGROUND

Serum cystatin C increasingly is used as a marker of glomerular filtration rate and cardiovascular risk. However, information for serum cystatin C levels in the general population, specifically across a wide age range and different ethnicities, is lacking.

OBJECTIVES

To determine nationally representative serum cystatin C levels, estimate the prevalence of increased cystatin C levels in the general population, and identify factors associated with increased cystatin C levels.

STUDY DESIGN

Cross-sectional survey.

SETTING AND PARTICIPANTS

A nationally representative subsample of 7,596 participants aged 12 years or older in the Third National Health and Nutrition Examination Survey conducted in 1988-1994.

PREDICTORS

Age, sex, race/ethnicity, risk factors for chronic kidney disease.

OUTCOMES

Continuous serum cystatin C levels and serum cystatin C level greater than 1.12 mg/L.

MEASUREMENTS

Cystatin C was measured in 2006 from stored sera by using an automated particle-enhanced nephelometric assay.

RESULTS

Overall median serum cystatin C level was 0.85 mg/L. Median cystatin C levels increased steeply with age and were greater in males and non-Hispanic white persons, even in a healthy subgroup of 20- to 39-year-olds. Prevalences of increased serum cystatin C levels (>1.12 mg/L) were 1%, 41%, and greater than 50% in all persons aged younger than 20 years, 60 years or older, and 80 years or older. In persons aged 60 years and older, older age, non-Hispanic white ethnicity, hypertension, current smoking, lower levels of education and high-density lipoprotein cholesterol, and increased body mass index, C-reactive protein, and triglyceride values were associated significantly with increased serum cystatin C levels.

LIMITATIONS

No measured glomerular filtration rate, single measurement of cystatin C, cross-sectional study design.

CONCLUSIONS

Serum cystatin C level is related to sex and ethnicity, even in young healthy individuals. The prevalence of increased cystatin C levels increases dramatically with age, reaching greater than 50% after the age of 80 years in both sexes and all ethnic groups.

Xa inhibition and coagulation activity--the influence of prolonged dalteparin treatment and gender in patients with acute coronary syndrome and healthy individuals

BACKGROUND

We evaluated coagulation activity in relation to gender in patients with acute coronary syndromes and in healthy individuals of similar age, and related coagulation activity to levels of Xa inhibition during dalteparin treatment.

METHODS

Serial blood samples were obtained from 555 (172 women) of 2267 patients in the Scandinavian FRISC II study, and a single sample in 457 (151 women) apparently healthy age- and sex-matched individuals. After randomization, all patients received dalteparin 120 IU/kg s.c. (maximum 10,000 IU) twice daily for 5 to 7 days inhospital and thereafter placebo (n = 285) or sex- and weight-adjusted doses of dalteparin (5000 or 7500 IU) twice daily (n = 270) for 3 months.

RESULTS

Before randomization, 96% of the patients had open-label anticoagulation with unfractionated heparin or dalteparin. Therapeutic anti-Xa levels (> 0.5 IU/mL) were found in 74%, 55%, 58%, and 33% of the dalteparin-treated patients at randomization, 2 days, 4 to 7 weeks, and 3 months, respectively, and were significantly related to lower levels of coagulation activity, ie, factor VIIa, prothrombin fragment 1+2, and D-dimer, during prolonged treatment. Female patients had higher anti-Xa levels than men at randomization (median 0.69 vs 0.60 IU/mL, P = .01) and at 2 days (0.65 vs 0.59 IU/mL, P < .001). Female patients had also significantly higher levels of all 3 coagulation markers at randomization, 2 days, 4 to 7 weeks, and 3 and 6 months. Similarly, healthy women had higher prothrombin fragment 1+2 levels (median 1.19 vs 0.94 nmol/L) and D-dimer levels than men (26 vs 21 microg/L) (both P < .001).

CONCLUSIONS

Despite weight-adjusted dosing, female patients reached higher anti-Xa levels, suggesting increased sensitivity to dalteparin treatment. Healthy women and female patients also had higher coagulation activity, which might increase the risk of thrombus formation. The large proportion of patients with subtherapeutic anti-Xa during prolonged dalteparin treatment may reflect poor compliance and could thus contribute to the gradual loss of clinical efficacy.

Amino-terminal pro-B-type natriuretic peptide: analytic considerations

Amino-terminal pro-B-type natriuretic peptide (NT-proBNP) is a convenient molecule to work with in clinical laboratories, with preanalytic and analytic advantages, such as excellent stability at different temperatures, flexibility in sample type, and strong harmony across all commercially available NT-proBNP assays (including recently released point-of-care methods). Another major advantage of NT-proBNP assays is that they show excellent analytic precision. Reference values for NT-proBNP testing are strongly affected by the population tested. Among nondiseased populations, lower values are expected, whereas in diseased populations, such as in patients with acute dyspnea, higher reference values are more useful. Also, the biologic variability of NT-proBNP should be taken into account to evaluate the significance of any change in its values. When analyzed in patients with stable heart failure, biologic variability was 25%-40%. This article reviews the laboratory aspects of NT-proBNP testing from the perspective of the clinical laboratorian.

Plasma homocysteine is elevated in elderly patients with memory complaints and vascular disease

BACKGROUND

There is an association between elevated plasma total homocysteine (tHcy) and vascular disease in elderly patients suffering from organic and non-organic mental disease. The main objective of the present study was to investigate the relationship between plasma tHcy concentration and vascular disease in elderly patients with memory complaints.

METHODS

In 108 patients with memory complaints the concentration of plasma tHcy was related to the presence of vascular disease. Furthermore, different determinants of plasma tHcy concentration were measured.

RESULTS

Patients with confirmed memory complaints (CMC, n = 86) which fulfilled the criteria of mild cognitive impairment were divided into two categories, with and without vascular disease. The CMC group without vascular disease showed similar biochemical and brain imaging findings to patients with subjective memory complaints (SMC, n = 22). The group of CMC patients with vascular disease had higher age, higher plasma tHcy, lower serum folate and lower renal function than patients without vascular disease.

CONCLUSION

The finding of two subgroups of patients with CMC supports the notion that mild cognitive impairment is a heterogenous clinical entity with multiple aetiological factors. The elevated plasma tHcy in the group of CMC patients with vascular disease is likely to be associated with vascular disease.